1. Field of the Invention
This invention relates to a fluid-contacting process which uses a plurality of types of particle, such as a catalyst, in which the contacting is stopped, the particles mixed and separated. In another aspect, this invention relates to the separation, regeneration and return of a catalyst in a multi-catalyst catalytic conversion process.
2. Description of the Prior Art
In fluid-contacting processes, careful attention must be paid to the design of vessels and to the size of particles used in these vessels, in order to achieve maximum activity, effectiveness and life with minimum operating cost. In general, in vapor, liquid, or mixed-phase operation, smaller particles are preferred for better access of the fluid to all active surfaces within the particle, thus providing better effectiveness and life. However, larger particles are desired to reduce pressure drop, resulting in corresponding lower compression costs and vessel costs. These opposing objectives require an optimizing decision in the process design. These considerations are applied to processes such as sorption, ion exchange, catalytic conversion, etc., in which a fluid may be contacted with two or more different types of particle.
As the level of technology involved in fluid contacting processes becomes increasingly more sophisticated, the use of more than one type of contacting particle in a given process is becoming more common, especially when one of the types performs a different function from the other, e.g., a guard bed for a sorption bed or a catalyst bed. With special reference to catalytic processes, it is often advantageous to have more than one type of catalyst in a given reactor or in a reactor containing a plurality of beds. These different catalysts may differ initially in chemical composition or in physical properties such as pore size or surface area. The different catalysts may be tailored for different specific reactor locations, such as the top, middle or bottom of the reactor catalyst charge.
Eventually it will become necessary to empty the reactor, for such reasons as contamination or deactivation of the catalyst particles, or inspection of the internals of the reactor or reactors containing the catalyst. On emptying such a reactor, it is very difficult to avoid intermixing of the previously layered, different catalysts. Such intermixing is frequently undesirable for various reasons, including the lack of suitability of the mixture for reuse after ex-situ regeneration, the need for different regeneration conditions for one or more of the different catalysts, or loss of value in subsequent metals recovery because of higher metals recovery costs due to mixtures of hard-to-separate metals.
Separation of such mixed catalyst systems by physical separation methods, such as screening, is commonly practiced using catalysts of the same general shape but different dimensions--for example, mixtures of small and large cylindrical extrudates, balls, or tablets. However, use of bigger catalyst particles for one type of catalyst in the system would reduce catalytic effectiveness and activity, and the use of smaller catalyst particles would increase pressure drop and operating cost.
It is also known from the art to conduct a catalytic reaction using catalysts which have a polylobal shape. For example, U.S. Pat. Nos. 3,990,964; 3,966,644; and 3,674,680, which are incorporated herein by reference, describe catalysts having various polylobal shapes including dumbbell, figure eight, "C", trilobal, cross, clover leaf and tetralobal.